Various special effects are used in displaying video images in television. One kind of special effect involves a reduction in the size of an image as seen on a screen. Other kinds of special effects involve enlargement, or rotation of the image. Such effects generally include scaling the image in some way and these effects will be generally referred to as transforming the shape of a video image on a screen.
In the case of reducing the shape of a video image by conventional techniques, wherein the bandwidth of the video signal is reduced by a comparatively large filter prior to compression in time and expansion in the frequency domain, such pre-filtering must be carried out before the compression to reduce "aliasing", i.e. degradation of picture quality. Compression has the effect of "folding back" the components of the signal and it is necessary to attenuate sufficiently any frequencies which will be folded back, since they would otherwise be manifested as undesirable frequency components that cause aliasing. Besides the cost and complexity of using large filters, if it is necessary to achieve a high quality image, then it would also be necessary to use a comparatively large interpolating circuit with sharp roll-off frequencies. Such a circuit can also be costly and complex.
When transforming a video image to create other special effects, similar and other problems exist when using conventional techniques.
The present invention generally seeks to provide an improvement in the resolution of a horizontal component of a digital video signal which is used in a technique of transforming a video image on a screen. In the case where the transformation is a reduction in image size, other advantages can be obtained in the form of a simplification of circuitry as long as certain design parameters are not exceeded.